I have a 4640 with quad range that appears to be leaking/gaining hydraulic oil into the motor. Haven't talked with to many people that have seen this. It definitely smells and seems to be hydraulic and not fuel. Also does not appear to be water as i let it set and cracked drain plug. I've heard it could possibly be leaking behind oil pan at the 1/2 moon gasket?? Also, obviously have heard the rear main seal. Tractor has roughly 5300 hours. Just curious if anyone else has experienced this. Thanks